[Solved] This is how I stopped Child Maintenance with 50/50 shared care
@samaugier in short, if CMS have sent you a payment plan, they would expect you to pay. if you stop paying, then they can switch to collect any pay, then add on additional 20% enforcement charge. you could look at appealing the rejected mandatory reconsideration, by applying to tribunal. have 1 month to appeal the MR if they reject it. I have come across cases where CMS have arranged refunds for a paying parent, where they over-paid/wrongly paid.
you could also consider putting a complaint into their senior manager: firstname.lastname@example.org can also copy in your local MP to email.